Hantavirus Outbreaks: From War Trenches to Cruise Ships

During the Korean War, around 3,200 United Nations soldiers came down with a fever that could cause hemorrhaging in the kidneys and other parts of the body. Reports of similar diseases in Eurasia date back thousands of years, but at the time, the cause of the illness was still unknown. In the 1970s, South Korean virologist Ho Wang Lee was finally able to identify the virus that caused the disease. He isolated the virus in mice near the Hantan River, which is how it became known as the “Hantaan virus.”

Today, the term “hantavirus” refers to the Hantaan virus and several other viruses that cause two distinct illnesses in humans. The first illness is hemorrhhagic fever with renal syndrome, or HFRS. This is the disease that afflicted U.N. soldiers during the Korean War, and it has a mortality rate of less than 15 percent.

The second illness is hantavirus pulmonary syndrome, or HPS, a deadlier respiratory condition that scientists first identified in the Americas in the 1990s. Humans can catch both HFRS and HPS from inhaling aerosols from rodent urine and feces. Although rare, some forms of HPS have been transmitted between humans, and it has a mortality rate of up to 50 percent.

The hantavirus that killed three passengers of an Oceanwide Expeditions cruise ship in the spring of 2026 was the kind that causes HPS and can spread between humans (which might be how it reached the ship in the first place). But there is a longer history of soldiers contracting HFRS in Europe and Asia during wartime, when they might have come into close contact with rodents carrying hantaviruses.

In 1942, around 1,000 German soldiers and 60 Finnish soldiers in Salla, Finland, came down with a disease that did not appear to spread from human to human. Recent research suggests the disease was likely hemorrhagic fever with renal syndrome caused by the Puumala virus, a hantavirus that scientists identified in 1980.

But how did these soldiers end up contracting the virus? Jens H. Kuhn, a virologist who has written about the history of hantavirus classification, says many aspects of war can bring rodents into closer contact with people, leading to infections. Bombing, trench digging and other changes to the environment can send rodents searching for food in trenches, barracks and other locations, leaving behind waste that humans can come into contact with.

“These animals would poop all over the trenches, and the soldiers will have slept in the trenches, so they will be constantly exposed to this kind of stuff,” he says.

According to 1940s medical reports about the World War II outbreak in Finland, three-fourths of the soldiers who became sick were on the front lines and likely living in poor conditions. The reports also noted that soldiers frequently encountered rodents in trenches and cabins.

The larger HFRS outbreak that occurred among U.N. troops in Korea between 1951 and 1954 caused serious concern among military leaders, and researchers have continued to investigate hantavirus infections in the context of war. During the 1990s wars in the Balkans, soldiers became sick with HFRS from at least two different hantaviruses. In addition, the authors of a paper published in Military Medicine in 2024 note that hantaviruses are present in some rodents in Ukraine, making the ongoing Russian war a possible source of future infections.

In 1993, a young couple in New Mexico died within days of each other after experiencing the same unexplained respiratory illness. The virus that killed them was initially known as the “Four Corners virus” after the region in the southwestern United States. Researchers later renamed it the Sin Nombre virus—Spanish for “without name”—and identified it as a type of hantavirus that causes a different illness from those found in Europe and Asia.

Since then, researchers have discovered multiple other hantaviruses in North and South America. Like the Sin Nombre virus, all of these Western Hemisphere viruses cause hantavirus pulmonary syndrome, which is more deadly than hemorrhagic fever with renal syndrome. In addition, one New World hantavirus, the Andes virus, can spread between humans.

HPS received renewed attention in the United States in 2025. That year, actor Gene Hackman and his wife, Betsy Arakawa, died at their home in Santa Fe, New Mexico, under unusual circumstances. Investigators later revealed that Arakawa had died of hantavirus pulmonary syndrome, though it is still unclear how she became infected. (Hackman, who had Alzheimer’s disease, died later from heart disease.)

One year later, hantavirus pulmonary syndrome received international attention due to an outbreak on an Oceanwide Expeditions cruise ship. On April 11, 2026, a Dutch passenger died aboard the ship from what authorities later identified as hantavirus pulmonary syndrome caused by the Andes virus. Within a month, his wife died in South Africa, and another German passenger died aboard the ship.

The cruise ship outbreak prompted international efforts to quarantine and track people who were still aboard or had already left the ship in an attempt to contain the outbreak. It also highlighted the unique risk posed by the Andes virus because of its ability to spread between humans.